import matplotlib.pyplot as plt
import numpy as np

x = np.linspace(-3,3,50)
y1 = 2*x + 1
y2 = x**2

plt.figure()
plt.plot(x,y2)
plt.plot(x, y1,color='red', linewidth=1.0, linestyle='--')
# 取值范围
plt.xlim((-1,2))
plt.ylim((-2,3))
plt.xlabel('I am x')
plt.ylabel('I am y')

new_ticks = np.linspace(-1,2,5)
print(new_ticks)
plt.xticks(new_ticks)

plt.yticks([-2,-1.8,-1,1.22,3,],[r'$really\ bad$',r'$bad\ \alpha$','normal','good','really good'])

# 将右边和上边的轴取消
# gca = 'get current axis'
ax = plt.gca()
ax.spines['right'].set_color('none')
ax.spines['top'].set_color('none')

ax.xaxis.set_ticks_position('bottom')
ax.yaxis.set_ticks_position('left')

ax.spines['bottom'].set_position(('data',0))
ax.spines['left'].set_position(('data', 0))


plt.show()